3rd GPU not recognized by windows.

[MagicBit15]

I have 2 5870's installed. Put them both in perfect. Have a dummy plug in one, works great, is recognized by windows and hashes just fine.

Got a third card, same 5870. Put it in, when i turned on windows it said installing new hardware thing. It said complete. Boom only the first two are recognized.

The riser works, It is 18 inches long, it is 16x, and I tried it in another card with two cards and it works fine. I have a dummy plug in the new card as well.

I read something about windows only recognizing two legacy drivers. Can I only use this dummy plug for one of the cards. Or should I just dump all this and try linux.

I am getting frustrated. Anything would help.

[hyphenated]

I presume that your first two cards are plugged straight into the mobo.

18" is *very* long for a riser - especially a 16x.  Is it powered (ie does it have a molex at the top)?  Have you plugged the Molex in to +12V?  Do the card fans start up with the mobo?

Try swapping the last card for your second (known working ) card.

Try going back to two GPUs but use the riser for the second known working card.

How big is your PSU?  Are you stretching it too far?  Check the 12V current capabilities.